Progressive global warming legislation in the European Union (EU) and the United States (US) is constantly driving automotive Original Equipment Manufacturers (OEMs) to seek an environmentally friendly refrigerant for use in mobile climate control applications. The traditionally used refrigerant, R134a, is a fluorinated greenhouse gas (F-gas) with a high Global Warming Potential (GWP) of 1,430. The EU Directive 2006/40/EC requires mandatory phase-out of R134a by Jan. 1, 2017, for passenger and light commercial vehicles. In the US, the Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA) have developed the One National Program to reduce greenhouse gas emissions and improve fuel economy. Most recently, EPA has listed R134a as unacceptable for newly manufactured light-duty vehicles beginning in Model Year 2021 with limited exceptions.
The synthetic refrigerant, R1234yf, is introduced as a near drop-in alternate to R134a with a relatively low GWP of 4 and similar thermodynamic properties. A limited supply of R1234yf and a high price, however, have created concern and some OEMs consider R1234yf to be an interim replacement while continuing to study other solutions, R744 (carbon dioxide) offers another option due to its low cost, nonflammability, high volumetric heat capacity, and perhaps most importantly, environmental friendliness, i.e., R744 is a natural substance having an ODP=0 and a GWP=1.
System performance in terms of energy efficiency and effectiveness in cooling and heating is another driver for new climate control technology. Operation of mobile air conditioning (MAC) units could consume 10% or more fuel for gasoline and diesel engines. For hybrid and electric vehicles, the heat pump technology is gaining popularity due to significantly improved heating efficiency compared to electric heating methods. The R134a or R1234yf heat pump systems, however, suffer from poor performance and sub-atmospheric pressure operation for low ambient conditions below −20 degrees Celsius. While the R744 system circumvents this drawback, its cooling efficiency decreases as the ambient temperature rises. The existing R744 systems are generally considered useful below approximately 40 degrees Celsius. Accordingly, a need exists for a system utilizing an environmentally friendly refrigerant that overcomes the noted limitations and operates efficiently in both warm and cold regions.
Preferably, the system would utilize a refrigerant having low GWP values, such as the natural refrigerant R744, and maintain its efficiency regardless of ambient temperature. In other words, the system should operate efficiently for low ambient conditions below −20 degrees Celsius, high above 40 degrees Celsius, and all conditions in between. The system should also be able to be implemented in all types of vehicles including hybrid and electric vehicles, in hybrid and electric vehicles, the system should increase, if not significantly increase, driving ranges. Similarly, fuel economy for gasoline and diesel vehicles should improve.